1. Field of the Invention
The present invention is related to a dustproof structure for a sleeve bearing. More particularly, the present invention is related to the dustproof structure having a dustproof cushion attached to the oil-impregnated sleeve bearing to thereby ensure circulating lubricant.
2. Description of the Related Art
Referring to FIG. 1, a conventional bearing structure for a motor consists of an axial seat 10, a motor stator 20, a motor rotor 30. The axial seat 10 is combined with an axial tube 11 in which to accommodate a sleeve bearing 12, and on which to couple the motor stator 20. In assembling, a shaft 31 of the motor rotor 30 extends through an axial hole 120 of the sleeve bearing 12 so that the motor rotor 30 is rotatably connected to the axial seat 10. Generally, lubricant contained in the sleeve bearing 12 may be driven due to rotation of the shaft 31. The lubricant successively flows through an inner circumference of the axial hole 120, an end surface of the sleeve bearing 12, an inclined surface 121 of the sleeve bearing 12, and a gap between the axial tube 11 and the sleeve bearing 12. Finally, the lubricant returns to the inside of the sleeve bearing 12. Thus, the lubricant contained in the sleeve bearing 12 is automatically circulated to maintain the inner circumference of the axial hole 120 so as to attenuate abrasion of the axial hole 120 caused by rotation of the shaft 31. Consequently, it reduces rotational noise and prolongs useful life of the bearing.
Although the lubricant of the sleeve bearing 12 is able to attenuate abrasion, discharging the lubricant from the axial tube 11 is unavoidable while operating. Foreign dust may enter the inside of the sleeve bearing 12 and the gap between the axial tube 11 and the sleeve bearing 12. Thus, it results in precipitation of the foreign dust on the sleeve bearing 12 and the gap between the axial tube 11 and the sleeve bearing 12 that produces greasy dirt 90. Circulating the lubricant on the sleeve bearing 12, the greasy dirt 90 is collected or precipitated in a space formed on the inclined surface 121 of the sleeve bearing 12. Once the greasy dirt 90 enters the gap between the axial tube 11 and the sleeve bearing 12, the circulation of the lubricant can be obstructed. Thus, the lubricant cannot flow freely through between the axial tube 11 and the sleeve bearing 12 and it results in an insufficiency of the lubricant between the axial hole 120 and the shaft 31. The rotational speed of the motor is reduced and the running temperature of the motor is increased. Consequently, the shaft 31 of the motor may be jammed and the useful life of the motor is shortened. Hence, there is a need for an improvement of the conventional bearing structure.
To this end, U.S. Pat. No. 6,336,745, titled “OIL-IMPREGNATED BEARING AND ROTOR SHAFT,” and U.S. Pat. No. 6,435,722, titled “COMBINATION STRUCTURE FOR OIL-IMPREGNATED BEARING,” discloses a conventional bearing structure include an axial seat, a motor stator, a motor rotor, an axial tube and an oil-impregnated bearing. The bearing structure further includes a cap disposed on an end surface of the oil-impregnated bearing, and a shaft of the motor rotor includes a cushion ring arranged between the cap and the oil-impregnated bearing. The oil-impregnated bearing has a plurality of oil-guiding grooves on its outer circumference for circulating lubricant. In rotational operation, the cap and the cushion ring are commonly used to prevent leaking lubricant from the oil-impregnated bearing, and entering dust into the oil-impregnated bearing. However, the combination of the cap, the cushion ring and the oil-impregnated bearing results in the disadvantage that assembly of the motor's members is complicated. After assembling, an end edge of the cap closely abuts against an end surface of the oil-impregnated bearing, which obstructs lubricant flow to the oil-guiding grooves and reduces efficiency for cycling the lubricant. Thus, it results in an insufficiency of the lubricant between the axial hole and the shaft. The rotational speed of the motor is reduced and the running temperature of the motor is increased. Consequently, the shaft of the motor may be jammed and the useful life of the motor is shortened. Hence, there is a need for an improvement of the conventional bearing structure.
The present invention intends to provide a dustproof structure for a sleeve bearing which includes an axial tube to accommodate a sleeve bearing and a dustproof cushion. At least one oil-returning groove is formed between the sleeve bearing and the dustproof cushion to prevent from entering foreign dust and to ensure cycling the lubricant in such a way to mitigate and overcome the above problem.